1. Field of the Invention
The present invention relates generally to microwave crisping and browning of foods via a disposable packaging element which will produce a heating effect when exposed to microwave energy, as well as packages and methods utilizing such elements.
2. Background Art
As manufacturers of prepared foods attempt to meet the marketplace demand for increasing numbers and varieties of prepared foods which can be heated in a microwave oven, they have experienced problems associated with enabling the product to be heatable in a microwave oven without resulting in areas that are either overcooked or undercooked, while also ensuring that the heated product will possess the desired degree of browning or crispness that such foods normally have when cooked in a conventional oven, particularly when the product is one requiring browning or crisping of multiple and nonplanar surfaces.
Various forms of specialized packages have been developed which are designed to achieve microwave browning of food cooked therein. Such packaging involves the use of a film or element that will convert microwave energy into thermal energy so as to produce a browning and/or crisping of an item of food situated in heat exchange contact therewith. In some cases the food is disposed within an outer package body that is used for shipping and storage as well as for heating of the food product. In other cases, the food is disposed on a tray-like member that is situated within an outer package body for shipping and storage, but is removed or rearranged relative to the outer package body when the food item is to be heated.
A first type of packaging that is used for both shipping and storage as well as heating of items of food is represented by Brastad U.S. Pat. Nos. 4,267,420 and Brastad, et al. 4,230,924. In these patents, flexible sheets of microwave interactive materials are wrapped closely about individual items of food so that when the package is exposed to microwave energy, at least a portion of the microwave energy impinging the package will be converted into heat for browning the surface of the food. However, such packages have been found to pose problems with various types of food which give off heat, grease or vapor. Furthermore, some irregularly shaped foods may be difficult to wrap without unacceptable bunching of the sheet material.
A second type of package that is used for both shipping and storage as well as heating of items of food is disclosed in Turpin, et al. U.S. Pat. No. 4,190,757. In the package and method in accordance with this patent, a microwave interactive layer is provided for contacting the underside of a food product and a second interactive layer may be provided to contact the top surface thereof, as well. The problem of venting of moisture is resolved through the provision of openings in the outer package body that are covered for shipping and storage purposes, but may be exposed for heating of the food product. However, for foods which do not have planar bottom or bottom and top surfaces, and food products requiring browning at side surfaces as well, uniform browning or crisping cannot be achieved with such a package. Likewise, due to the fixed configuration of the package body, for example, a package suitable for heating of a sandwich may not be suitable for heating of a turnover or pocket-type pie.
A cook-in package which not only deals with the problem of venting of foods which will give off grease or vapor during heating, but also deals with the problem of obtaining more uniform browning of foods on multiple nonparallel surfaces is disclosed in commonly assigned, copending U.S. application Ser. No. 829,227, filed Feb. 14, 1986. In this application, a package assembly is disclosed which includes a microwave interactive tray, having a bottom wall and one or more opposed side walls, is designed to have a nonrectangular cross-sectional configuration suited for closely conforming to the cross-sectional profile of a food product to be browned or crisped in it during heating in a microwave oven. Furthermore, for venting purposes, the tray is provided with vent openings and is open-ended. However, even though this package assembly is very effective for microwave heating of certain products, such as French bread pizzas, the tray of the package assembly cannot be utilized independent of the outer package body of the assembly and is not suitable for microwave heating of such products as waffles and sandwiches requiring browning of top as well as bottom and side surfaces thereof.
In U.S. Pat. Nos. 4,555,605, and Divisional Patent thereof 4,612,431, a package assembly and method for storing and microwave heating of food is disclosed which includes, as a component of the package assembly, a disposable tray having a microwave interactive layer thereon, which is usable independent of the outer package body of the package assembly. However, the tray of this package assembly is only suitable for obtaining browning or crisping of a substantially planar bottom surface of a food product.
Thus, there is a need for a packaging element which can be utilized independent of an outer package body, yet is still capable of browning top, bottom and side surfaces of a food product. Furthermore, for purposes of compactly packaging such an element within a package assembly, it is desirable that the element be collapsible from a configuration conforming to the shape of a food item to be heated therein to a generally flat configuration for shipping and storage purposes. Moreover, it is considered to be particularly desirable to achieve an element of the noted type which can be utilized with food items of both rectangular and nonrectangular cross-sectional profiles.